The effects of hormones on the induction of ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC), and polyamine levels in vivo are being studied. Previous studies have shown that ODC induction may be a marker for tumor promoters. Hormones often increase the biological activities of complete carcinogens. ODC is used to study the degree of biochemical similarity between hormones and promoters. The present studies indicate that estradiol induces renal ODC and SAMDC in both the rat and hamster. This observation may explain in part the carcinogenic activity of estrogens to hamster kidney. ODC levels in the ovary and uterus of female rats vary with the estrus cycle and are inversely correlated with each other. Estrogens as potential promoters will be tested in two-stage initiation-promotion carcinogenesis studies.